/*
 * Copyright (C) 2012 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package interactivespaces.util.io.directorywatcher;

import interactivespaces.system.InteractiveSpacesEnvironment;

import java.io.File;
import java.util.Set;
import java.util.concurrent.TimeUnit;

/**
 * Watch a directory for additions and deletions of files.
 * 
 * @author Keith M. Hughes
 */
public interface DirectoryWatcher {

	/**
	 * Start the watcher up.
	 * 
	 * @param environment
	 *            the spaces environment being run under
	 * @param period
	 *            how often the directories should be scanned
	 * @param unit
	 *            time unit for the scanning period
	 */
	void startup(InteractiveSpacesEnvironment environment, long period,
			TimeUnit unit);

	/**
	 * Start the watcher up and scan the directories immediately.
	 * 
	 * <p>
	 * The listeners will not be called with the files returned.
	 * 
	 * @param environment
	 *            the spaces environment being run under
	 * @param period
	 *            how often the directories should be scanned
	 * @param unit
	 *            time unit for the scanning period
	 *            
	 * @return the initial set of files in all scanned folders
	 */
	Set<File> startupWithScan(InteractiveSpacesEnvironment environment, long period,
			TimeUnit unit);

	/**
	 * Shut down the watcher.
	 */
	void shutdown();

	/**
	 * Add a new directory to watch.
	 * 
	 * @param directory
	 *            the directory to watch
	 * 
	 * @throws IllegalArgumentException
	 *             the supplied file is either not a directory or is not
	 *             readable
	 */
	void addDirectory(File directory);

	/**
	 * Add a new listener to the watcher.
	 * 
	 * @param listener
	 *            the listener to add
	 */
	void addDirectoryWatcherListener(DirectoryWatcherListener listener);

	/**
	 * Remove a listener from the watcher.
	 * 
	 * <p>
	 * Nothing is done if the listener was never added
	 * 
	 * @param listener
	 *            the listener to remove
	 */
	void removeDirectoryWatcherListener(DirectoryWatcherListener listener);

	/**
	 * Force a scan of the registered directories.
	 */
	void scan();
}
